Electromagnetic shielding is provided at joints between removable panels of housings for electronic equipment and testing facilities to impede transmission of electromagnetic fields. Optimally, the shielded item is isolated from the effects of external circuitry and other sources of electromagnetic disturbances. Electromagnetic shielding is often required for shielded enclosures such as, for example, doors of electronic laboratory rooms, casings of radio transmitters, receivers and computers and other similar facilities and equipment.
Commonly, such structures and equipment require shielding along gaps between surfaces of doors, access panels, drawers, cabinets or the like, where surfaces are repeatedly, or only possibly, moved relative to one another. For example, electrical components may be arranged individually in cases which are slid into and out of cabinets every time there arises a need to test, service or update the component. Accordingly, it is highly desirable for the casing to have electromagnetic shielding that is adapted to withstand the bi-directional shearing action induced upon it by each insertion and removal of the casing into and from the cabinet. Similarly, electrical components may be arranged in a compartment accessible only through a pivoting door which must be opened and closed each time there arises a need to test, service or update the component. As with the casings, it is highly desirable for the mating surfaces of the door to have electromagnetic shielding that is adapted to withstand the "wiping" action induced thereon during each pivot of the door. Failing such characteristics, the electromagnetic shielding of the electrical component may become broken and the component along with the entire electrical system to which it is connected becomes vulnerable to electromagnetic interference.
One prior shielding arrangement is disclosed in U.S. Pat. No. 3,504,095 issued Mar. 31, 1970 to Roberson et al. In a preferred embodiment, the Roberson patent discloses an electromagnetic gasket including a curved bearing portion and a longitudinal attaching portion connected to one side of the curved bearing portion. A plurality of notches divide the curved bearing portion into a row of integral fingers along the entire length of the gasket. These fingers have free ends which are capable of being snagged and/or bent excessively. Also, the other ends of the fingers are held rigidly in place relative to one of the shielded surfaces so that the gasket offers more resistance to shear or "wiping" in one transverse direction than in the opposite one.
Another prior shielding arrangement is disclosed in U.S. Pat. No. 3,277,230, issued on Oct. 4, 1966 to Stickney et al. The Stickney et al. patent discloses an electronic shielding gasket that includes a linear metallic strip having a central portion with spaced holes for receiving a special fastening device and fingers extending outwardly in rows from opposite edges of the central portion of the gasket. The free ends of both rows of fingers are left exposed and unprotected from being snagged upon one of the surfaces to be shielded when the surfaces are slid transversely relative to each other and to the gasket. Mounting of the Stickney et al. gasket also requires a relatively substantial amount of space due to the lateral extension of the fingers in opposite directions.
Other types of electromagnetic shielding arrangements, including those with longitudinal or circular strips arranged upon one of the opposed surfaces, are disclosed in U.S. Pat. Nos. 2,825,042 issued Feb. 25, 1958 to Tollefson et al.; 2,844,644 issued July 22, 1958 to Soule Jr.; and 3,904,810 issued Sept. 9, 1975 to Kraus.
Another known joint seal for electromagnetic wave shielding includes contact springs having a generally V shaped cross-section and providing an electromagnetic seal between a pair of movable members. The contact springs extend from one movable member at equal angles from beneath a clamp which is attached to the movable member. An arrangement of this type is disclosed in U.S. Pat. No. 3,962,550 issued June 8, 1976 to Kaiserswerth. Being asymmetrical, the Kaiserswerth device is not well-suited to effect electromagnetic shielding between two members which slide bi-directionally with respect to each other.
In IBM Technical Disclosure Bulletin Vol. 20, No. 1, page 281 (June 1977), a conductive seal for electromagnetic shielding is disclosed which is usable between movable panel sections. The seal comprises a transversely arched rubber strip whose upper surface is laminated with a metal foil. The flattened longitudinal edges of the laminated rubber strip are held in place by a metal strip 6 having longitudinal edge regions curled upwardly about the longitudinal edges of the laminated rubber strip.
In the IBM arrangement, the longitudinal ends of the rubber strip are confined such that the compliant deflection of the assembly occurs almost entirely in the arched portion of the laminated rubber strip. Accordingly, it is desirable to have the laminated metal foil relatively thin and yet suitably bonded to the rubber layer so as to remain attached even under excessive and repeated deflection of the rubber strip.
In U.S. Pat. No. 4,623,752 issued to Steen et al. on Nov. 18, 1986, a double-action gasket assembly for EMI/RFI shielding is disclosed having an elongated, articulated structure mounted on a substantially planar carrier. The articulated structure is formed of segments having an arcuate section with opposed extensions bent toward each other to form a respective pair of coplanar sections. The carrier is situated beneath the arcuate section and is contiguous with the coplanar sections. The carrier includes a means for mounting the gasket assembly to a mounting surface such as the edge of a panel.